The purpose of the study is to identify objectively the behavioral patterns associated with organic characteristics found through intensive medical work-ups of children referred for hyperactivity. Each parent of a referred child independently completes a behavior checklist from which a standardized behavior profile is derived. Degree of inter-parent agreement is computed and the profiles are analyzed in order to classify children according to types of behavior patterns. Classification of children in this way is then compared with the outcomes of the medical work-up to determine whether the behavioral typology corresponds to characteristics of the children identified clinically.